<template>
	<ul class="list">
		<li class="item" 
		v-for="index of letters" 
		:key="index" 
		:ref="index" 
		@click="handleLetterClick" 
		@touchstart="handleTouchStart" 
		@touchmove="handleTouchMove" 
		@touchend="handleTouchEnd" 
		>{{index}}</li>
	</ul>
</template>

<script>
export default {
	name: 'CityAlphabet',
	props: {
		'cities': Object
	},
	data(){
		return {
			timer: null
		}
	},
	computed:{
		letters(){
			const letters = []
			for(let i in this.cities){
				letters.push(i)
			}
			return letters
		}
	},
	updated(){
		this.startY = this.$refs['A'][0].offsetTop
	},
	methods: {
		handleLetterClick(e){
			this.$emit('change', e.target.innerText)
		},
		handleTouchStart(){
			this.touchstart = true
		},
		handleTouchMove(e){
			if(this.touchstart){
				if(this.timer){
					clearTimeout(this.timer)
				}
				this.timer = setTimeout(() =>{
					const touchY = e.touches[0].clientY - 79
					const index = Math.floor((touchY - this.startY) / 20)
					if(index >=0 && index < this.letters.length) {
						this.$emit('change',this.letters[index])
					}
				},15)
			}
		},
		handleTouchEnd(){
			this.touchstart = false
		}
	}
}	
</script>

<style lang="stylus" scoped>
@import '~styles/varibles.styl'
.list
	display: flex
	flex-direction:column
	justify-content: center
	position: absolute
	right: 0
	top: 1.58rem
	bottom: 0
	width: 0.4rem
	.item
		line-height: .44rem
		text-align: center
		color:$bgColor
</style>